1. Field of the Invention
The present invention relates to a polyimide resin, widely known as a heat resistant resin, and more particularly, to a polyimide film having improved thermal dimensional stability
2. Description of the Related Art
It is known that polyimide resins exhibit excellent properties such as a high resistance to heat and chemicals, as well as having good electrical and mechanical characteristics. A polyimide film formed of a polyimide resin synthesized from 4,4'-diaminodiphenyl ether and pyromellitic dianhydride has been used in a wide variety of applications, such as is described in, for example, Japanese Patent Publication (Kokoku) No. 36-10999. Polyimide film, which exhibits excellent mechanical characteristics, such as in relation to elongation, has a high coefficient of expansion and thus poor thermal dimensional stability. In recent times, there has been a sharp increase in demand, especially on the part of the electronic and electrical industries, for a polyimide film having excellent dimensional stability and mechanical characteristics. This is because such a film would be extremely useful for printed circuit boards requiring fine processing, as well as in other fields, such as high density magnetic recording. For this reason, various studies are currently being made in an attempt to develop a polyimide film having excellent dimensional stability. For example, the use of rigid molecules such as paraphenylenediamine, dimethyl benzidine, and pyromellitic dianhydride for improving thermal dimensional stability is exemplified in Japanese Patent Disclosures (Kokai) Nos. 61-264028; 61-241325; 61-181828; 61-158025; and 58-185624. However, all of the resultant polyimide films leave room for further improvement with respect to their mechanical strength (particularly, elongation) and their resistance to heat and chemicals.